GB2058965A

GB2058965A - A differential mechanism

Info

Publication number: GB2058965A
Application number: GB8029247A
Authority: GB
Original assignee: Alsacienne de Constructions Mecaniques SA
Current assignee: Alsacienne de Constructions Mecaniques SA
Priority date: 1979-09-20
Filing date: 1980-09-10
Publication date: 1981-04-15
Also published as: DE3035264A1; IT1133120B; FR2465929A1; FR2465929B1; IT8024790A0; CH638282A5; GB2058965B

Abstract

The mechanism comprises two coaxial sun gears 1, 2 coupled respectively to two planetary pinions 4, 5 by means of two timing belts 6, 7. The planetary pinions 4, 5 are keyed on an eccentric shaft 14 rotatably mounted in a lightweight disc 3 which has the function of a planet carrier and is mounted to rotate freely on a central shaft 11. The two planetary pinions 4, 5 and the two sun gears 1, 2 are placed on each side of the disc, one sun gear 12 being rigidly fixed whilst the other 1 is capable of rotating freely. Another timing belt 21 is disposed in meshing engagement with the toothed rim of the disc. <IMAGE>

Description

SPECIFICATION A differential mechanism This invention relates to differential mechanisms of the type comprising two sun gears disposed in coaxial relation with a toothed annulus, the annulus being adapted to carry two planetary pinions coupled respectively to the two sun gears.

In known mechanisms of this type, the meshed pinions are of steel or of plastic material and must rotate in an oil bath which is enclosed within a sealed casing. If this requirement were not met, the pinions would be capable of transmitting only very low torques. When they are of metal, pinions of this type must be carefully ground and this constitutes a very costly machining operation. In spite of this precaution, the pin ions still produce a very high level of noise.

The aim of the invention is to provide a differential mechanism which is not attended by the above-mentioned disadvantages of known mechanisms.

To this end and in accordance with the invention, the coupling between each of the two planetary pinions and the corresponding sun gear is constituted by a timing belt. This arrangement dispenses with any further need either to ensure that the teeth of gears and pinions rotate in an oil bath or to grind the gear teeth. Even in the unground state as produced directly by a gear-cutting machine, the gear and pinion teeth cooperate with drive belts having "cogs" or teeth of trapezoidal section, each drive belt being provided with an internal reinforcement which is capable of ensuring the desirable strength and dimensional stability. By reason of the large number of teeth in mesh, mechanisms of this type are capable of transmitting high values of torque.

Finally, the operation of timing belts is noiseless.

In accordance with another feature of the invention, the toothed annul us of the mechanism is constituted by the rim of an aluminium disc which forms a planet carrier. Thus the said planet carrier has very low inertia which offers only slight resistance to accelerations, especially to reversals of direction.

A more complete understanding of the invention will be gained from the following description, reference being made to the accompanying drawing which is a view in perspective showing by way of example a typical embodiment of a differential mechanism in accordance with the invention.

The differential mechanism illustrated in the drawing comprises two sun gears 1, 2 in coaxial relation with a disc 3 which is adapted to carry two planetary pinions 4, 5 coupled respectively to the two sun gears 1, 2 by means of two timing belts 6, 7.

One of the two sun gears, namely the gear 1, for example, is rotatably mounted so as to be loose on a central shaft 11 which may be capable of rotating freely within bearings (not shown in the drawings). The disc 3 is also mounted so as to be loose on the said central shaft. The other sun gear 2 is rigidly fixed on the central shaft 11 by means of a key 12, for example. The two planetary pin ions 4, 5 are rigidly fixed respectively on the two ends of a shaft 14 which is parallel to the central shaft 11 and is freely rotatable within a bearing formed by a boss 1 5 of the disc 3. Both the axial interval between the two sun gears 1, 2 and the axial interval between the two planetary pinions 4, 5 have been considerably exaggerated for the sake of enhanced clarity of illustration.In actual practice, however, the said gears and pinions would be positioned respectively against the lateral faces of the hub 17 and of the boss 15 of the disc 3.

The disc 3 is of light metal such as aluminium which is preferably anodized and provided in the form of a relatively thin web 1 8 having a hub 17, the rim 19 of the said web being cut in the form of a toothed wheel on which another timing belt 21 is intended to engage.

The advantages attached to the particular structure of this differential mechanism will not be further discussed here since they have already been explained in the foregoing. It may be added, however, that the mechanism operates as a planetary speed reduction unit when the disc 3 is not rotating.

1. A differential mechanism comprising two coaxial sun gears and two coaxial planetary pinions coupled together respectively by means of timing belts, characterized in that the planet carrier is constituted by a single disc, the said two planetary pinions being keyed on an eccentric shaft rotatably mounted in the said disc, that the said two planetary pin ions are placed symmetrically on each side of the surface of the disc, that the said disc is mounted to rotate freely on a central shaft which carries the two sun gears, one gear being rigidly fixed to the central shaft and the other gear being mounted to rotate freely on the said central shaft, and that the two sun gears are disposed symmetrically on each side of the said disc.

2. A mechanism in accordance with claim 1, characterized in that the disc aforesaid is composed of a thin lightweight web and of a toothed rim so shaped as to receive a timing belt.

3. A mechanism in accordance with claim 2, characterized in that the disc is of light metal such as aluminium which is preferably anodized.

4. A differential mechanism, substantially as hereinbefore described with reference to and as illustrated in the accompanying draw

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A differential mechanism This invention relates to differential mechanisms of the type comprising two sun gears disposed in coaxial relation with a toothed annulus, the annulus being adapted to carry two planetary pinions coupled respectively to the two sun gears. In known mechanisms of this type, the meshed pinions are of steel or of plastic material and must rotate in an oil bath which is enclosed within a sealed casing. If this requirement were not met, the pinions would be capable of transmitting only very low torques. When they are of metal, pinions of this type must be carefully ground and this constitutes a very costly machining operation. In spite of this precaution, the pin ions still produce a very high level of noise. The aim of the invention is to provide a differential mechanism which is not attended by the above-mentioned disadvantages of known mechanisms. To this end and in accordance with the invention, the coupling between each of the two planetary pinions and the corresponding sun gear is constituted by a timing belt. This arrangement dispenses with any further need either to ensure that the teeth of gears and pinions rotate in an oil bath or to grind the gear teeth. Even in the unground state as produced directly by a gear-cutting machine, the gear and pinion teeth cooperate with drive belts having "cogs" or teeth of trapezoidal section, each drive belt being provided with an internal reinforcement which is capable of ensuring the desirable strength and dimensional stability. By reason of the large number of teeth in mesh, mechanisms of this type are capable of transmitting high values of torque. Finally, the operation of timing belts is noiseless. In accordance with another feature of the invention, the toothed annul us of the mechanism is constituted by the rim of an aluminium disc which forms a planet carrier. Thus the said planet carrier has very low inertia which offers only slight resistance to accelerations, especially to reversals of direction. A more complete understanding of the invention will be gained from the following description, reference being made to the accompanying drawing which is a view in perspective showing by way of example a typical embodiment of a differential mechanism in accordance with the invention. The differential mechanism illustrated in the drawing comprises two sun gears 1, 2 in coaxial relation with a disc 3 which is adapted to carry two planetary pinions 4, 5 coupled respectively to the two sun gears 1, 2 by means of two timing belts 6, 7. One of the two sun gears, namely the gear 1, for example, is rotatably mounted so as to be loose on a central shaft 11 which may be capable of rotating freely within bearings (not shown in the drawings). The disc 3 is also mounted so as to be loose on the said central shaft. The other sun gear 2 is rigidly fixed on the central shaft 11 by means of a key 12, for example. The two planetary pin ions 4, 5 are rigidly fixed respectively on the two ends of a shaft 14 which is parallel to the central shaft 11 and is freely rotatable within a bearing formed by a boss 1 5 of the disc 3. Both the axial interval between the two sun gears 1, 2 and the axial interval between the two planetary pinions 4, 5 have been considerably exaggerated for the sake of enhanced clarity of illustration.In actual practice, however, the said gears and pinions would be positioned respectively against the lateral faces of the hub 17 and of the boss 15 of the disc 3. The disc 3 is of light metal such as aluminium which is preferably anodized and provided in the form of a relatively thin web 1 8 having a hub 17, the rim 19 of the said web being cut in the form of a toothed wheel on which another timing belt 21 is intended to engage. The advantages attached to the particular structure of this differential mechanism will not be further discussed here since they have already been explained in the foregoing. It may be added, however, that the mechanism operates as a planetary speed reduction unit when the disc 3 is not rotating. CLAIMS

4. A differential mechanism, substantially as hereinbefore described with reference to and as illustrated in the accompanying draw ing.

5. A differential mechanism comprising two coaxial sun gears and two coaxial planetary pin ions coupled together respectively by means of timing belts.

6. A differential mechanism according to any preceding claim characterized in that said timing belts each comprise a body of natural or synthetic rubber or of a plastics material having embedded therein a reinforcement comprising a woven or non woven textile material or steel cords or steel filaments, said timing belts being provided with teeth on their inner surfaces for meshing engagement with said gears.